Such electrical connecting means are used e.g. for cardiac pacemakers, the implanted pacemaker device being connected to a lead system inserted into the heart, as well as for implantable defibrillators, implantable pumps for metered administration of drugs, e.g. insulin, and devices for stimulating the muscles and nerves.
In the field of implantable cardiac pacemaker technology, considerable change has taken place in recent years. The use of modern microprocessor technology has allowed the systems to become much smaller, on the one hand, and greatly increased their efficiency in processing biomedical signals, on the other hand. The reduction in size of implantable pacemakers made it necessary to reduce the size of the connecting means between the can and the lead system accordingly. Whereas the connecting means between the implantable lead and the pacemaker can had an outside diameter of five or six millimeters in the area of the plug in the early pacemakers this diameter is now in the range of 3.2 millimeters. At the end of 1987 an international convention was worked out with the goal of unifying an electrical connecting means with plug diameters of 3.2 millimeters. On Jan. 27, 1989, such a standard, the so-called IS-1 Standard, was presented in a communication from the IEC/ISO International Pacemaker Standard Working Group IEC SC 62D/WG6 ISO TC 150/SCWG2. This standardized electrical connecting means can be used both for unipolar and for bipolar pacemaker and is now being produced by virtually all manufactures of cardiac pacemakers.
The plug of this electrical connecting means has a front contact pin having a first diameter of slightly less than 1.6 millimeters, an adjacent insulator with sealing elements and a diameter of about 2.6 millimeters, and a following cylindrical contact ring therebehind that is coaxial with the front contact pin and also has a diameter of about 2.6 millimeters. This is followed by another insulator that passes into the lead system and comprises appropriate sealing elements. The contact pin and the contact ring are provided with electrical leads that are run in the lead system and designed e.g. as mutual insulated and banked coils. The socket for the plug has a stepped bore adapted to the diameters of the plug and in which corresponding contact surfaces are provided for the front contact pin and the contact ring.
The use of one connecting means for either unipolar or bipolar pacemaker systems complies in particular with the clinical finding that bipolar pacemaker systems are better protected against interference effects. While polar pacemaker systems involved numerous negative aspects in the past so that unipolar systems were frequently preferred, the disadvantages of bipolar pacemaker systems have now been eliminated so that these systems can now be given preference. A survey on this can be found in the article by E. Alt, "Kritischer Vergleich uni- und bipolarer Schrittmachersysteme," published in Zeitschrift fur Kardiologle 76, 1987, p. 189-194.
Pacemaker systems having a plurality of additional intracardiac or intravascular electrode points have also been proposed in recent years. Within one lead it is thus possible to measure e.g. the atrial potentials in the atrium; cf. D. E. Antonioli et al. in C. Meere, Cardiac pacing PACE Symposium, Montreal 1967. A more precise detection of the atrial potentials with additional electrode points i.e. more than two within a pacing lead inserted into the heart has been described in the past by several authors. These additional electrode points in the heart, whose electrical leads are run within the lead system for the pacing lead, are connected to the pacemaker in such a way that a plurality of separate electrode plugs are connected to the pacemaker can. Pacemaker leads with a plurality of electrode points wherein the electrode leads are bifurcated and connected to a plurality of plugs are also known in the field of cardioversion; cf. U.S. Pat. No. 4,499,907.
With the increasing clinical use of rate adaptive cardiac systems, the implantation of additional sensors in the human organism has acquired growing clinical importance. EP-A No. 10178 528 describes a cardiac pacemaker system in which additional electrodes are used to measure the systolic pressure or its time derivative in the right ventricle. The electrical leads for the electrodes are run within the lead or probe for the pacing electrode and end in a plug received in a socket in the pacemaker can. The electrical contact between the plug and the socket is established via a plurality of contact rings on the plug and corresponding contact surfaces in the socket. This patent also describes the possibility of surrounding a front central contact pin by a plurality of satellite pins which are considerably smaller than said pin. The socket then has additional receiving sockets for these satellite plugs. Such an electrical connecting means can establish electrical contacts necessary for the pacemaker system described therein, but the plug is incompatible with standardized electrical connecting means of the aforesaid type and cannot be built with such small diameter as the currently used bipolar IS-1 Standard connector. A further major drawback is the complicated isolation of all these additional satellite plugs.
In bipolar pacemaker systems equipped with additional sensors, e.g. for measuring the blood temperature or the blood oxygen content, and therefore always requiring more than the two contacts available in the electrical connecting means, the line leading from the pacing lead and the additional sensors is therefore opened so that the lines for the additional sensors end in a separate plug which is introduced into an additional socket in the pacemaker can. The same applies to pacemaker systems having a plurality of sensors for measuring a corresponding plurality of parameters, which are being developed at a forced pace at present; cf. e.g. E. Alt et al., "A new Rate Modulated Pacemaker System--Optimized by Combination of Two Sensors" in PACE Vol. 11, 1119-1129, August 1988.
Defibrillators also require measured values from a plurality of sensors for correctly detecting the indication for defibrillation. Such parameters are not only electrical variables but increasingly also hemodynamic parameters which are detected by appropriate sensors.
Neurostimulators also stimulate not only in the area of one neuromere but in the area of a plurality thereof, so that here, too, a plurality of electrical leads are required which must be connected to a corresponding implant containing a control circuit.
Furthermore, implantable devices are being increasingly used for treating metabolic changes, e.g. diabetes mellitus. In the latter case, the administration of insulin with the aid of an implantable micropump is controlled partly via sensors which are connected by electrical contacts to the implant containing a control circuit and the pump. Here, too, a plurality of leads is required.
Further electrical connecting means having more than two contacts are known from U.S. Pat. Nos. 4,603,696, 4,236,525, 4,527,605, 4,323,081, 4,268,725, 4,411,277, 4,245,642, 4,411,276 and 4,538,623. All these models are special fabrications or improvements which can only be connected to a specially produced implantable medical device. None of these connecting means is compatible with devices obeying the aforesaid standard for electrical connecting means. It is therefore desirable to provide a universally applicable connecting means which is compatible with standardized connecting means. This is of general relevance in those cases, where a lead with more than two contacts and a special sensor is implanted for a given medical indication in a given patient. In the timely course there might be change in the clinical status of the patient and a standard bipolar connection as discussed would be preferable to connect a standard device to the formerly implanted special lead.
A further major concern is the isolation of a third pole. Since it is most likely that any kind of sensor that yields typically very small voltages might be connected, a high degree of isolation such as more than 100 kilo Ohms, preferably even more than 0.5 Megohm Ohm, is mandatory for correct function. In order to achieve an isolation of this order, improved sealing means are needed. Since implantable devices are getting smaller and smaller, bulky insulation on the outside of a connector increases the size of the whole connecting means intolerably.
It is therefore a major aim of this invention to provide excellent sealing means for a third connection without increasing the size of a connection system over the size that is used with the aforediscussed standard. Conventional kinds of contact and sealing structure on the outside of a connector cannot solve the aforementioned requirements. The present invention givens a solution to those requirements.